Researchers at the University of Illinois at Urbana-Champaign have developed a way in which a spacecraft can use pulsar star signals to navigate in space.

The remnants of a collapsed neutron star, called a pulsar, are magnetically charged and can rotate anywhere from one revolution per second to hundreds of revolutions per second. These celestial bodies, each 12 to 15 miles in diameter, generate light within the X-ray wavelength spectrum. Researchers from University of IllinoisUrbana-Champaign has developed a new way in which a spacecraft can use signals from multiple pulsars to move into deep space.

Pulsar stars

“We can use star trackers to determine the direction of the spacecraft, but to find out the exact location of the spacecraft, we rely on radio signals sent between the spacecraft and Earth. This can be time consuming and requires the use of an oversubscribed infrastructure, such as NASA’s Deep Space Network, “said Zach Putnam, a professor in the Department of Aerospace Engineering at the University of Illinois.

Professor Zachary Putnam

“The use of X-ray navigation eliminates these two factors, which until now required the initial forecast position of the spacecraft as a starting point. This study presents a system that finds candidates for possible spacecraft locations without prior information so that the spacecraft can navigate autonomously.

“In addition, our terrestrial communications systems for deep space missions are currently overloaded. This system will give autonomy to the spacecraft and reduce dependence on the earth. X-ray pulsar navigation surrounds this and allows us to determine where we are without calling.

Emissions of electromagnetic radiation

Since our atmosphere filters all X-ray emissions, you will need to be in space to observe them. Pulsars emit electromagnetic radiation, which is similar to pulses, because scientists can measure the peak in X-ray signals each time the pulsar rotates and points toward the Earth – like a beam of light cast by a beacon on a lighthouse.

Pulsar stars
Intersection of band areas of three pulsars in 3D.

“Each pulsar has its own characteristic signal, like a fingerprint,” Putnam added. “We have X-ray records of about 2,000 pulsars over time and how they have changed over time.

Like the global positioning system, the location can be determined from the intersection of three signals.

“The problem with pulsars is that they spin so fast that the signal repeats itself a lot,” Putnam said. “By comparison, GPS is repeated every two weeks. With pulsars, although there are an infinite number of possible spaceship locations, we know how far these candidate locations are from each other.

“We are looking to determine the position of the spacecraft within domains that have diameters of the order of many astronomical units, such as the size of Jupiter’s orbit. The challenge we are trying to deal with is how to intelligently monitor pulsars and fully determine all possible locations of a spacecraft in a domain without using excessive computing resources.

Finding the positions of spaceships

The algorithm, developed by graduate student Kevin Lohan, combines observations from multiple pulsars to determine all possible positions on the spacecraft. The algorithm handles all candidate intersections in two or three dimensions.

“We used the algorithm to study which pulsars we need to monitor in order to reduce the number of candidate spacecraft locations in a given domain,” Putnam concluded.

The results revealed that observing sets of pulsars with longer periods and small angular distances can significantly reduce the number of candidate decisions in a domain.

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Spacecraft utilised x-rays from pulsars to navigate in deep space

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